Coating system for asphalt and related methods

ABSTRACT

A coating system and related methods for an airfield surface or a roadway is described. The coating system may include a stable cationic emulsion for application to the airfield surface or the roadway. The stable cationic emulsion may include a) an asphalt blend comprising gilsonite, wherein the gilsonite is modified to possess a positive charge, b) one or more polymers, and c) one or more surfactants not including a cationic surfactant. The coating system may also include a fine aggregate material for application to the stable cationic emulsion applied to the airfield surface or the roadway.

TECHNICAL FIELD

The present disclosure relates to a coating system and related formethods for asphalt pavements.

BACKGROUND

Asphalt pavement is a composite material that includes mineral aggregateand an asphalt binder which hardens to form a robust surface. Asphaltpavement deteriorates over time from oxidation of the asphalt binder,heavy loads, and varying climatic conditions. One method for restoringor repairing deteriorated asphalt pavement is to remove and replace theexisting pavement with either newly prepared or recycled pavement.Removal and replacement, however, is expensive and wasteful. Thereexists, however, asphalt pavement maintenance products that are used torepair pavement surfaces.

A typical asphalt maintenance product includes a coating composition,such as a uintaite-asphalt composition, and an aggregate. In general,the composition may be spray applied to the asphalt pavement and theaggregate is then applied over the composition using spreaders or othersimilar devices. There are however many variations in how thecomposition and aggregate can be formulated. The components of thecomposition, type of aggregate, and the application rates (gals./yd²and/or lbs./yd²) can all be varied to accomplish certain performanceobjectives. Furthermore, in some cases, the coating composition andaggregates may be combined together and then applied to the pavement. Inlarge part, however, the specific product applied to the pavement andits application rate is dependent on how the pavement is used.

The asphalt pavement industry has two somewhat separate sectors:aviation/airfield and roadway. Aviation pavements have greater demandscompared to roadway pavements. For aviation pavements, safety isparamount, construction operations and schedules are difficult toimplement, and problems are more critical and more costly to address.Additionally, the airfield pavements are used to support airplaneswhereas roadways are used for cars and trucks. The two pavements typesalso age differently. In general, the requirements for aviationpavements (e.g. performance requirements, specifications, qualitycontrol systems, etc.) are generally tighter and more extreme than thoseused for roadway pavements.

Common roadway asphalt maintenance surface treatments are not alwayssuitable for airfield pavements. Common roadway treatments designed fordurability beyond 3-5 years are typically not suitable for the requiredairfield pavements. As roadway treatments increase in age they alsocreate safety-performance problems, e.g. creation and increase offoreign object debris (FOD) and decrease in positive frictioncharacteristics. In situations where the airfield asphalt pavement, evenif previously treated with a common uintaite-asphalt coating or anothermaintenance coating, begins to decay in terms of its surface-conditioncharacteristics, then it must be treated again in order to maintain theminimum safety requirements. If no further treatment is applied, thenthe pavement must undergo a much more significant and expensivedisruptive rehabilitation procedure. Common roadway treatments can bemodified to improve roadway condition and increase the frictioncharacteristics, thereby addressing the safety issues described above.Unfortunately, such treatments have a relatively brief lifespan, lasting2-5 years or less. Other more substantial (heavily applied) asphaltmaintenance treatments may provide a service-life of more than 3-5years. However, those substantial treatments are less suitable for therequirements of airfield pavement applications. There is a lack ofcoating systems that can be applied at relatively heavier rates that aresuitable in both roadway and aviation pavements, and have increasedbeneficial life.

SUMMARY

An embodiment of the present disclosure is a coating system for anairfield surface or a roadway. The coating system may include a stablecationic emulsion for application to the airfield surface or theroadway. The stable cationic emulsion may include a) an asphalt blendcomprising gilsonite, wherein the gilsonite is modified to possess apositive charge, b) one or more polymers, and c) one or more surfactantsnot including a cationic surfactant. The coating system may also includea fine aggregate material for application to the stable cationicemulsion applied to the airfield surface or the roadway.

Another embodiment of the present disclosure is a method ofmanufacturing a stable cationic asphalt emulsion. The method includesblending an asphalt cement with gilsonite to form an asphalt blend. Themethod also includes preparing an aqueous solution comprising water, amodifier, and one or more surfactants, wherein none of the one or moresurfactants is a cationic surfactant. The method further includescombining the asphalt blend with the aqueous solution to form a cationicemulsion, thereby giving rise to positive charge on a portion of thegilsonite so as to form the stable cationic emulsion. The method alsoincludes adding one or more polymers to the aqueous solution or thecationic emulsion.

Another embodiment of the present disclosure is a method for applying acoating system to a surface. The method includes spraying with aapplicator vehicle a stable cationic emulsion on to a surface. Thestable cationic emulsion has a) an asphalt blend comprising gilsonitewith the gilsonite modified to possess a positive charge, b) one or morepolymers, and c) one or more surfactants not including a cationicsurfactant. The method also includes applying a fine aggregate at a rateof at least 1.0 lbs per square yard onto the stable cationic emulsionapplied to the surface.

Another embodiment of the present disclosure is a system for coating asurface. The system includes a spraying unit for spraying the stablecationic emulsion. The system also includes a spreader unit mounted tothe applicator and configured to apply the fine aggregate to thesurface. The spreader unit includes a hopper to hold the fine aggregatematerial, a controllable gate coupled to the hopper, the controllablegate being moveable to allow the fine-aggregate to exit the hopper, anda roller assembly near the controllable gate configured to apply thefine aggregate material onto the sprayed emulsion.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofillustrative embodiments of the present application, will be betterunderstood when read in conjunction with the appended drawings. Forpurposes of illustrating the present application, there is shown in thedrawings illustrative embodiments of the disclosure. It should beunderstood, however, that the application is not limited to the precisearrangements and instrumentalities shown. In the drawings:

FIG. 1A is schematic of an applicator vehicle and a spreader unit usedto apply the fine aggregate material to the surface in accordance withan embodiment of the present disclosure;

FIG. 1B is schematic of a spreader unit shown in FIG. 1A;

FIG. 1C is a perspective view of a portion of a roller assembly in thespreader unit shown in FIG. 1B;

FIG. 1D is a side view of the portion of the roller assembly in thespreader unit shown in FIG. 1C;

FIG. 2A is schematic of an applicator vehicle and a spreader unit usedto apply the fine aggregate material to the surface in accordance withan embodiment of the present disclosure;

FIG. 2B is schematic rear view of a spreader unit shown in FIG. 2A;

FIG. 2C is schematic side view of the spreader unit shown in FIG. 2A;

FIG. 2D is schematic rear view of a spreader unit according to anotherembodiment of the present disclosure;

FIG. 2E is schematic side view of the spreader unit shown in FIG. 2D;and

FIG. 3 is schematic of an applicator vehicle and a spreader unit used toapply the fine aggregate material to the surface in accordance with anembodiment of the present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of the present disclosure include a coating system forapplication to an airfield surface or a roadway surface and methods ofmaking components of such a coating system. Embodiments of the presentdisclosure also include systems and methods for applying the coatingsystem to an airfield surface or a roadway surface. The inventiveconcepts herein include a coating system comprised of a stable cationicemulsion and a fine aggregate material for application to the stablecationic emulsion that is applied to the airfield surface or theroadway. The stable cationic emulsion may include an asphalt blendcomprising gilsonite. In various embodiments, gilsonite includescomponents that are modified to possess a positive charge, therebygiving rise to a stable cationic emulsion. The coating system has beenfound to be suitable for both aviation and roadway pavements, despitethe variance in end use requirements for each pavement type. Eachcomponent of the coating system will be described below.

The stable cationic emulsion may include an asphalt blend comprisinggilsonite, one or more polymers, and one or more surfactants that do notinclude a cationic surfactant. The emulsion may also include a modifier,such as acid, and water. The cationic emulsion is processed so that thegilsonite in the asphalt blend has cationic properties. This, in turn,permits use of non-cationic type surfactants. The presence of polymer(s)in the emulsion, surfactants, and modifier create a stable emulsion thatcan be stored for extended periods of time for later use. This allowsthe emulsion to be pumped into storage tanks and/or delivered to worksites over extended distances without degrading the efficacy of thecoating system when applied to the pavement surfaces.

The asphalt blends includes at least asphalt cement and gilsonite. Insome cases, additional additives, such as oils and surfactants, may beadded to the asphalt blend as processing aid or binders. Asphalt cementmay be described as a colloid system comprised various components. Forexample, the asphalt cement may include, asphaltenes, aromatics, resins,and oily/waxy saturates, among other components. In most cases, the hardasphaltenes are surrounded (solvated) by the aromatics, resins,oily/waxy saturates, etc. The asphalt blend may have certain parametersthat are preferable. In one example, the asphalt cement is 120/140penetration grade asphalt. The penetration grade is an assessment of howhard it is to penetrate it with a particular. The penetration grade forasphalt cement as used herein is measured in accordance with test methodASTM D-5. The asphalt blend can also have a colloidal index at least2.50 to ensure a good balance. Furthermore, the asphalt blend and theasphalt cement should have certain range of saturate, aromatic, resinand asphaltene (SARA) paramaters. See for instance, table 3 below. SARAanalysis method that divides crude oil components according to their(chemical group classes, of interest herein is) polarizability andpolarity. As used herein, the SARA analysis method used is ASTM D-2007.

Gilsonite is a naturally occurring asphaltite hydrocarbon mineral resin.Gilsonite is a unique composition that is known to be difficult tocompound into an asphalt emulsions. Gilsonite is a combination ofvarious molecules that act in asphalt compositions in a number ofdifferent ways. Gilsonite is known to be relatively high in polars andresins. For this reason, gilsonite can solvate asphaltenes typicallypresent in asphalt cement. Gilsonite also generally establishes a moreuniform spectrum to asphalt's colloid balance. Gilsonite is selected, inpart, because its colloidal properties balance well with the colloidalproperties of asphalt cement typically available.

The gilsonite in the asphalt blend has been modified (to) improveadhesion. Gilsonite has relatively high nitrogen content. The nitrogenin gilsonite is present as a pyrrole molecule (i.e. a polar resin) andthe addition of gilsonite increases the polar (polar resin) fraction ofthe asphalt blend as seen in the SARA analysis. The nitrogen pyrrole ingilsonite has certain beneficial characteristics. Because gilsonitecomprises nitrogen pyrroles, and pyrroles are non-toxic to livingorganisms, gilsonite is deemed environmentally beneficial. Furthermore,the presently disclosed inventive concepts capitalize on the presence ofnitrogen pyrroles. In certain embodiments, the nitrogen pyrroles aremodified to become a surfactant in the emulsion. By driving the pH ofthe emulsion down to an acidic state via presence of a modifier, such asan acid, the nitrogen pyrrole is activated to become a N+ positivelycharged molecule on the surface of the gilsonite-asphalt droplet. Thus,portions of the gilsonite possess a positive charge and behave as acationic surfactant. The modified gilsonite in combination with use ofnon-cationic surfactants supplies the desired cationic characteristic ofthe emulsion. The surprising result is a uniquely stable emulsion.Furthermore, this aspect also creates a gilsonite-asphalt droplet withan inherent adhesion property. It is believed that the cationic chargeof the gilsonite acts as an adherent, instead of relying on a surfactantfor adhesion as is used on typical asphalt emulsions. Cationic adhesionis a necessary property for adhesion of the asphalt droplet to thenegatively/anionic pavement surface. Table 1 below illustrate typicalmetals found in gilsonite in accordance with the present disclosure asmeasured with x-ray Fluorescence or XRF, which is used to grade theproduct's composition in regards to metals.

TABLE 1 Approximate Metal Content of Gilsonite Metal Approx. Max. ppm Na500 Mg 200 Al 550 Si 1600 Ca 350 Cu 1 Fe 450 Mo 11 Zn 15

The amount of asphalt blend in the emulsion can vary. In one example,the asphalt blend comprises between about 50.0% to about 70.0% by weightof the emulsion. In another example, the asphalt blend comprises betweenabout 55.0% to about 65.0% by weight of the emulsion. The amount ofasphalt cement in the asphalt blend is at least 85% by weight of theasphalt blend. In one example, asphalt cement is present in the asphaltblend at a level of at least 80% by weight of the asphalt blend. Thegilsonite may comprise at least 15% by weight of the asphalt blend. Inone example, gilsonite is present in the asphalt blend at a level of atleast 20% by weight of the asphalt blend. Furthermore, it should beappreciated that at these stated levels, the gilsonite may comprise atleast 10% by weight of the emulsion. In some cases, however, the asphaltblend and/or the amount gilsonite may comprise more or less than theranges stated above.

The emulsion may comprise one or more polymers. Polymers may be used toincrease the durability and toughness of the completed coating systemand aid in retaining fine-aggregate material in the coating applied tothe pavement. Exemplary polymers or copolymers include those that assistin providing desired properties for the asphalt emulsion residue, forexample by, providing a stress-absorbing layer that strongly adheres tothe underlying pavement, by providing a non-tacky surface, or byproviding a polymer with a non-swelling nature. In one example, thepolymers may include polymers and co-polymer combinations, such asacrylic, a styrene-butadiene rubber, or combinations thereof. Thepolymer or polymers may comprise between about 1.0% to about 5.0% byweight of the emulsion.

Exemplary acrylic polymers or copolymers are preferably derived fromacrylate monomers. The acrylate monomers may for example be based on(meth) acrylic acid, esters of (meth) acrylic acid, (meth) acrylamide,(meth) acrylonitrile and derivatives of these acrylate monomers.Exemplary esters of (meth)acrylic acids include, but are not limited to,alkyl and hydroxyalkyl esters, e.g., methyl (meth)acrylates, ethyl(meth)acrylates, butyl (meth)acrylates, hydroxyethyl (meth)acrylate,isobornyl (meth)acrylate, and longer chain alkyl (meth)acrylates such asethylhexyl (meth)acrylate, lauryl (meth)acrylate, cetyl (meth)acrylate,and stearyl (meth)acrylate. Derivatives of (meth)acrylamide include, butare not limited to, alkyl substituted (meth)acrylamides, e.g.,N,N-dimethyl (meth)acrylamide, N,N-dipropyl (meth)acrylamide, t-butyl(meth)acrylamide, N-octyl (meth)acrylamide, and longer chain alkyl(meth)acrylamides such as N-lauryl (meth)acrylamide and N-stearyl(meth)acrylamide. The acrylic polymers also include polymers commonlyknown as acrylics, acrylate polymers, polyacrylates or acrylicelastomers. Acrylate polymers belong to a group of polymers which couldbe referred to generally as plastics while acrylic elastomer is ageneral term for a type of synthetic rubber whose main component is anacrylic acid alkyl ester (for example, an ethyl or butyl ester).

Exemplary copolymers include polymers derived from polyolefins, such asvinyl acetate, vinyl chloride, vinylidene chloride, styrene, substitutedstyrene, butadiene, unsaturated polyesters, ethylene and the like. Insome embodiments, the acrylic copolymer is derived from acrylatemonomers and mixtures thereof and polymerized with styrene or ethylene.In still other embodiments, the acrylic copolymer is derived from butylacrylate and copolymerized with styrene or ethylene. In yet otherembodiments, the copolymer is an acrylonitrile butadiene.

The emulsion includes one or more surfactants. The surfactants establishappropriate stability, viscosity, and other necessary properties of theemulsion in storage, transport, application, set and cure. Thesurfactants also facilitate short-term and long-term enhancements of thepolymer binder to in the pavement.

The surfactants may be a non-ionic surfactant and an amphotericsurfactant. In most instances, however, the emulsion does not include acationic surfactant due to their detrimental impact on emulsionstability and reasons discussed elsewhere in the present disclosure.Accordingly, an amphoteric surfactant and/or non-ionic surfactants arepreferred in lieu of cationic surfactants. Amphoteric surfactants and/ornon-ionic surfactants boost the break/cure time of the emulsion whensprayed on the pavement. An amphoteric surfactant is one that can becationic at low pH and also anionic at high pH while non-inonics do notcarry specific charges. In contrast, a typical cationic surfactant, suchas a fatty alkylamine, is always cationic. Cationic surfactants have astrong positive charge except at very high pH. However, a strongpositive charge surfactant with gilsonite-asphalt blend as describedherein is problematic and counter-productive. For instance, a strongpositive charged surfactant destabilizes the emulsion over a short timeperiod, especially at gilsonite loadings of more than 8%-10% by weightof the asphalt blend. With gilsonite present at 20% by weight of theasphalt blend, an amphoteric surfactant provides a gentlebuffered-charge surfactant activity, which yields added stability.Furthermore, when the emulsion is sprayed on the pavement, an amphotericsurfactant accelerates the break/cure of the emulsion. In contrast, anon-ionic surfactant may indeed provide stability but also retards thebreak/cure of the emulsion when applied on the pavement. The presentemulsion surprisingly balances these competing features while avoidinguse of a cationic surfactant.

Exemplary amphoteric surfactants include, but are not limited to,alkoxylated alkylamine. Other eexemplary amphoteric surfactants includebetaines and amphoteric imidazolinium derivatives.

Exemplary non-ionic surfactants include ethoxylated compounds andesters, for example ethoxylated fatty alcohols, ethoxylated fatty acids,sorbitan esters, ethoxylated sorbitan esters, ethoxylated alkylphenols,ethoxylated fatty amides, glycerine fatty acid esters, alcohols, alkylphenols, and mixtures thereof. In one example, the non-ionic surfactantsmay be nonylphenol ethoxylate or ethoxylated alcohol.

The surfactants comprise between about 0.25% to about 4.0% by weight ofthe emulsion. In one example, the surfactants comprise between 0.25% toabout 2.5% by weight of the emulsion. Furthermore, the amphotericsurfactants comprise between about 0.25% to about 1.0% by weight of theemulsion. The non-ionic surfactants may comprise between about 0.25% toabout 4.0% by weight of the emulsion. In one example, the non-ionicsurfactants comprise between 0.5% to about 2.0% by weight of theemulsion. However, the surfactant levels are not strictly limited to thestated ranges above.

The emulsion may include modifier to charge the gilsonite in the asphaltblend. The modifier is present between 0.25% to 3.0% by weight of theemulsion. At this level, the pH of the emulsion is reduced to less than6.5 and preferably less than 5.0. A sub 6.5 pH level in the emulsion isindicative of charged gilsonite with the blend. As explained above, themodifier is used to drive the pH of the emulsion down to an acidic stateso that the nitrogen pyrrole within gilsonite is activated to become aN+ positively charged molecule. Accordingly, the emulsion includesmodified gilsonite that includes surfactant-like portions, which, inturn, improve stability and adhesion in use. The modifier may be anacid, such as hydrochloric acid.

The emulsion may contain other optional additives to adjust the emulsionproperties in relation to the planned use, application method, andstorage conditions. These include, for example, mineral salts,thickening agents, stabilizing agents, anti-freeze agents, adhesionpromoters, biocides, pigments and the like. However, the emulsion issubstantially free of tall oil pitch or coal tar.

In one example, the emulsion comprises, asphalt blend includinggilsonite at level between about 55%-70%; one or more polymers at levelbetween about 1%-5%; a nonionic surfactant at level between about0.5%-2%; an amphoteric surfactant at a level between about 0.25%-1.0%; amodifier, such as acid, at a level between about 0.5%-2.5%; and watercomprising the balance to 100% by weight of the emulsion.

The coating system also includes a fine aggregate material. The fineaggregate material may include, but is not limited to, crushed cherts,quartzites, or carbonates. Other types of fine aggregate materials maybe used as well. The fine-aggregate may be dry, clean, sound, durable,and angular shaped, with highly textured surfaces. In one example, thefine aggregate can comprise at least 50% of silicone dioxide by weightof the fine aggregate and up to about 5% of calcium oxide by weight ofthe fine aggregate.

The fine aggregate material is effective for improving surface frictioncharacteristics. The fine aggregate material may be easily and evenlyapplied with the emulsion onto the pavement at more substantial rates,e.g. at least 1.0 lb. per square yard. It is believed that uponapplication a significant proportion of the fine aggregate materialembeds in, and is sufficiently bound, within the emulsion as theemulsion sets and cures. The fine aggregate material remains embeddedsufficiently in order to provide enhanced friction and safetycharacteristics in the near-term as well as the long-term. The fineaggregate can have gradation limits shown in table 2 when tested inaccordance with ASTM C136. Furthermore, an exemplary fine aggregatematerial may include properties illustrated in table 3 further below.

TABLE 2 Fine Material Aggregate Particle Size Sieve DesignationPercentage by Weight Passing Sieves 12 100 14  98-100 16 85-98 30 15-4550 0-8 70 0-2 200 0-1

TABLE 3 Fine Aggregate Properties Test Test Method Range Micro-DevalASTM D7428 Up to 15% Magnesium Sulfate Soundness ASTM C88 - Fine Up to2% Aggregate LA Abrasion ASTIM C131 - Grading D Up to 8% Fine AggregateAngularity ASTM C1252 - Test At least 45% Method A Moisture Content (%)ASTM C566 Up to 2% Bulk Dry Specific Gravity ASTM C128 2.6-3.0 Bulk SSDSpecific Gravity ASTM C128 2.6-3.0 Apparent Specific Gravity ASTM C1282.6-3.2 Absorption (%) ASTM D2216 Up to 3% Mohs Hardness Mohs Scale Atleast 7.0 AIMS texture AIMS Texture Index At least 90% Polished StoneValue ASTM 3319 At least 65

In table 3, the Mohs hardness test is conducted according to standardtest ASTM MNL46 using the Mohs scale. AIMS texture was tested accordingto AASHTO TP81, the source aggregate was tested using No. 4 to ¼″ sizeparticles. Polished stone value was tested according to ASTM 3319,modified for fine aggregate using a source aggregate passing through a½″ sieve and retained on ¼″ sieve. The polished stone values are readusing the “F” scale per the test method. Preferably the fine aggregatematerial has sustainably 100% fractured faces measured according to ASTMD-5821 The fine aggregate material may also have a sand equivalentgreater than 85 tested according to ASTM D-2419.

The emulsion, without the addition of polymers, was also evaluated todetermine various parameters. The emulsion without the addition ofpolymers herein may have properties as indicated in table 4 below.

TABLE 4 Properties of Stable Cationic Emulsion Without Polymer(s)Property Text Method Value Saybolt Furol Viscosity at ASTM D244 20-100seconds 77° F. (25° C.) Residue by Distillation or ASTM D244 At least55% (57%) Evaporation Sieve Test ASTM D244 Up to 0.1% 24-hour StabilityASTM D244 Up to 1% 5-day Settlement Test ASTM D244 Up to 5.0% ParticleCharge ASTM D244 Positive pH 6.5 maximum pH Viscosity at 275° F. (135°C.) ASTM D4402 1750 cts maximum Solubility in 1, 1, 1 ASTM D2042 97.5%minimum trichloroethylene Penetration ASTM D5 50 dmm maximum AsphaltenesASTM D2007 15% minimum Saturates ASTM D2007 15% maximum Polar CompoundsASTM D2007 25% minimum Aromatics ASTM D2007 15% minimum

The complete emulsion, with polymers included, as described herein mayhave properties as indicated in table 5 below.

TABLE 5 Properties of Stable Cationic Emulsion With Polymer(s) PropertyTest Method Value Viscosity at 60° C. AASHTO T-315 up to 5000 ctsSoftening Point ° C. AASHTO T-53 At least 60 Penetration AASHTO T-4914-40 Elastic Recovery 25° C. AASHTO T-301 15%-75% Ductility 25° C.AASHTO T-51 5%-50%

Embodiments of the present disclosure include a method of making thestable cationic emulsion described above. Initially, the method includesblending asphalt cement with gilsonite to form the asphalt blend withcomponent ranges as described above. The blending may performed using astandard vat mixer or the like. This blending step may include adding anoptional gas oil, e.g. an atmospheric light oil, to the asphalt blend.The gas oil may assist the penetration of the emulsion into theunderlying pavement. Next, an optional surfactant is added to theasphalt blend. This optional surfactant is used to assist melting andblending of gilsonite in the asphalt blend. The asphalt blendcomposition at this stage is exposed to temperature of at least 300degrees Fahrenheit for a period of time. In one example, the asphaltblend is exposed to a temperature of about 350 degrees Fahrenheit andmixed, at the elevated temperature, for 24-48 hours.

The method includes, separately from forming asphalt blend, preparing anaqueous solution comprising water, the modifier (e.g. acid), and one ormore surfactant. As noted above, a cationic surfactant is not requiredin the aqueous solution. In one example, the acid is added to the waterfollowed by the surfactant(s). This aqueous solution is then mixed for aperiod of time.

The asphalt blend and aqueous solution are then pumped into an emulsionmill to form an emulsion. More specifically, the method includescombining the asphalt blend with the aqueous solution to form a cationicstable emulsion. As described above, the acid creates a more acidiccomposition and has the effect of creating a positive charge on portionsof the gilsonite in the asphalt blend, thereby forming the cationicemulsion with improved stability. The emulsion mill shears together thegilsonite-asphalt blend and the aqueous solution in a continuousprocess.

The method includes adding one or more polymers to the aqueous solutionor to the emulsion. For example, the polymer (s) may be added to theaqueous solution, i.e. the water phase of the emulsion prior to milling.Alternatively, the polymer (s) may be “post added” to the milledemulsion prior to loading into storage tanks or transport vehicles

The finished cationic emulsion may be pumped to the storage tanks andstored until needed. Because the cationic emulsion is stable, longerstorage times are possible. This improves inventory control and allowsthe compounder to be more reactive to demand. Furthermore, the abilityfor increased storage times does not adversely affect the set and cureproperties of the cationic emulsion when applied the pavement surface.

Another embodiment of the present disclosure is a system and method forapplying a coating system to a surface. The system and method can applythe coating system described above with an applicator vehicle 10modified to accommodate high aggregate loading levels. FIGS. 1A-3illustrate various embodiments of applicator vehicle used to applicationthe coating system. As shown in FIG. 1A, the applicator vehicle 10includes mounted thereon the spraying unit 20 and a spreader unit 30 sothat the emulsion and the fine aggregate, respectively, can beco-applied with a single vehicle. The applicator vehicle 10 alsoincludes a storage tank 12 that holds the cationic emulsion. Thespraying unit 30 is configured to spray the stable cationic emulsion atvarious application rates as described herein. The spreader unit 30 isconfigured to apply the fine aggregate to the surface. In oneembodiment, the spreader unit 30 includes a hopper 32 to hold the fineaggregate material and a controllable gate 34 coupled to the hopper 32.The controllable gate 34 is moveable to allow the fine-aggregate to exitthe hopper 32. The spreader unit 30 also includes a roller assembly 40near the controllable gate 34. The roller assembly 40 is configured toguide the fine aggregate material from the hopper 32 through thecontrollable gate 34 in order uniformly spread/drop the fine-aggregateonto the sprayed emulsion. The roller assembly 40 may include anelongate roller bar 42 (FIGS. 1B-1D) positioned inside a trough 44. Asshown, the roller bar 42 may include outwardly extending tines that runthe length of the roller bar 42. The roller bar 42 is operably coupledto a motor 46, which is used to rotate the roller bar 42. Thus, apreferred spreader unit may be referred to as roller unit orroller-spreader. The system optionally includes a means for assistingremoval of the fine aggregate material from the hopper. Such an optionalmeans may be an internal auger, a conveyor, or a vibrator or othersimilar device. The system also includes a controller configured tocontrol operation of the spreader unit and the sprayer unit. Thecontroller allows the operator of the applicator vehicle to control thefine-aggregate spreader unit in conjunction with the emulsion as thosecomponents are being applied to the surface.

FIGS. 2A-3 illustrate alternative embodiments of an applicator vehicle.Common parts and features between the applicator vehicle 10 shown inFIGS. 1A-1D and the applicator vehicle illustrated in FIGS. 2A-3 havethe same reference numbers. In accordance with one embodiment as shownin FIGS. 2A-2E, the applicator vehicle 10 includes a spinning spreaderunit 130 a with a hopper 132 a (FIGS. 2B and 2C). Accordingly, in lieuof the roller assembly, the spreader unit may include a spinning plate140 with fins (i.e. whirly spinner). Furthermore, a gate 134 a maydisposed toward the back of the hopper 132 a. In accordance with oneembodiment as shown in FIGS. 2D-2E, the applicator vehicle 10 includes aspinning spreader unit 130 b with a hopper 132 b. The spinning spreaderunit 130 b may include a spinning plate 140 with fins (i.e. whirlyspinner). However, the gate 134 may disposed toward the back of thehopper 132 a. Alternatively, as shown in FIGS. 2D and 2E, the gate 134 bmay be disposed below the hopper 132 b. In accordance with the disclosedembodiments, improved friction results have been obtained with thestandard “whirly spinner” units, albeit with some modifications.

In yet another embodiment illustrated in FIG. 3, the system mayalternatively be used with applicator vehicle 10 adapted to include anair driven spreader unit 230 as shown in FIG. 3. Accordingly, in lieu ofthe roller assembly, the spreader unit may include an air unit 240 whichis air-driven device to apply aggregate via air.

The method of applying the coating system includes spraying, with theapplicator vehicle, a stable cationic emulsion on to a surface. As notedabove, the stable cationic emulsion includes: a) an asphalt blendcomprising gilsonite, wherein the gilsonite is modified to possess apositive charge; b) one or more polymers; and c) one or more surfactantsnot including a cationic surfactant. In one example, the stable cationicemulsion is sprayed onto to surface at an amount of 0.10 to 1.0 gallonsper square yard. In another example, the stable cationic emulsion issprayed at an amount of 0.15 to 0.25 gallons per square yard.

The method also includes applying a fine aggregate at a rate of at least1.0 lbs per square yard onto the stable cationic emulsion applied to thesurface. In one example, the fine aggregate material is applied onto thestable cationic emulsion in an amount of from 1.0 lb per square yard to5.0 lbs per square yard. The stable cationic emulsion is sprayed via thesprayer unit mounted on the vehicle. And the fine aggregate is appliedwith spreader unit mounted on the same applicator vehicle. It should beappreciated, however, that it is possible to apply the stable cationicemulsion and the fine aggregate materials using more than one applicatorvehicle.

The present disclosure may be further understood with reference to thefollowing non-limiting examples.

Example 1

The cationic emulsion and fine aggregate material where prepared asdescribed herein. The spreader unit (whirly spinner version) was mountedon a standard asphalt distributor spray truck. The truck was set toapply from 1.0 to 3.0 lbs/SY of the fine aggregate material. Thecationic emulsion composition comprised about 60% by weight of theemulsion of the asphalt blend and about 2.5% by weight of the emulsionof a latex polymer (SB-acrylic). The fine aggregate material comprisedphysical properties as indicated in tables 2 and 3 above. In particular,the graded particle size was 100% passing a No. 14 US sieve. Thecationic emulsion was applied to an airfield asphalt pavement surfacewhich, prior to coating, was in “poor” condition according to thestandard the Pavement Condition Index (PCI). The cationic emulsion wasapplied to surface at 0.20 gallons per square yard and the fineaggregate material was applied at 1.5 pounds per square yard. Afterapplication and drying, the surface friction test was conducted. In thisinstance, friction testing proceeded according to Federal AviationAdministration (FAA) test method for continuous friction measuringequipment (CFME), FAA AC 150/5320-12. The FAA's CMFE standard is used toevaluate the friction value of an airfield surface and thus its safetylevel. This test provides a direct measure of surface friction against abraking tire and sets minimum values a surface must have to be FAAcompliant. The test revealed FAA CMFE 40 mph test value of 1.07 and 60mph value of 1.05. The tests were made after 6 days, after 34 days, andafter 160 days in order to gauge the consistency of the surface'sfriction over time and in presence of severe winter weather usingsnowplows. The measured values are recorded in table 6 below. Thecondition of the pavement, according the PCI, post application wasobserved as “significantly improved” to “good.” Thus, significantrecovery of the lost friction caused by the non-aggregate components ofthe cationic emulsion was achieved by adding 1.5 pounds per square yardof fine aggregate material. At this loading level, the coating system inexample 1 exceeded the FAA requirements for safety.

TABLE 6 Record Values from Test Conducted in Example 1 Control 40 mphControl 60 mph Test 40 mph Test 60 mph  6 days 1.07 1.05 0.89 0.91  34days 0.94 0.92 160 days 1.01 0.89

Example 2

In this example, the cationic emulsion and fine aggregate material wereprepared as in Example 1, with the exception being that for the emulsionthe polymer was an acrylic at a 2.0% level (by weight of the emulsion).The coating system was applied to an airfield asphalt runway pavementsurface which, prior to coating, was in “fair” condition. The coatingsystem was applied to six test areas using the application rates asshown table 7 below.

TABLE 7 Test Plan for Example 2 Cationic Emulsion Fine AggregateApplication Rate Application Rate Test Area (gal/yd²) (lb./yd²) 1 0.161.5 2 0.17 1.5 3 0.18 1.5 4 0.16 3.0 5 0.17 3.0 6 0.18 3.0

After application and drying, the friction was evaluated using the FAAAC CMFE procedure. The tests were made after 24 hours, and after 5 days,in order to gauge the consistency of the surface's friction over time.The measured values after application are shown in table 8 below. Thetests were conducted according to FAA AC 150/5320-12.

TABLE 8 Friction Data for Example 2 Test 24 hrs - Area 40 mph 24 hrs -60 mph 5 days - 40 mph 5 days - 60 mph 1 0.67 0.65 0.95 0.74 2 0.68 0.600.91 0.81 3 0.70 0.70 0.9 0.73 4 0.81 0.75 1.05 0.94 5 0.80 0.71 0.920.93 6 0.78 0.75 1.05 0.94

As can be seen in FIG. 3 and table 8, a significant recovery of the lostfriction caused by the non-aggregate components of the emulsion wasachieved by adding 1.5 lb./yd² of aggregate at the three differentcationic emulsion rates. In this example, the results exceeded the FAArequirements for safety, in addition to observing significantimprovement in pavement condition using the PCI. In addition, at therate of 3.0 lb./SY of aggregate, the coating system actually increasedthe overall friction of the pavement beyond the pre-treatment level andup into the highest level achievable. Data at this level is believed tocorrelate to that of a new pavement. This is a surprising result forsuch relatively low fine-aggregate levels.

The inventive concepts described herein have several benefits andsurprising results. The inventive coating systems attain improvedfriction characteristics that have not been observed in typical pavementcoating applications with light to medium (or higher) applicationlevels. For example, there are limits in the current practice ofseal-coating surfaces at these loading levels. For one, the applicationof a thicker coating systems on the pavement necessitates a) aconcomitant increase in the amount of aggregate materials applied, andb) use of a larger particle. However, the typical aggregates approvedfor use (by various governmental agencies) are not suitable for such“thicker” applications. Furthermore, existing applicator vehicles arenot designed to apply the aggregate uniformly at levels of 1.0 lbs persquare yard or greater. In addition, regardless of the amount ofaggregate applied to pavement, the higher rate of application ofconventional asphalt emulsions can still result an unacceptable level ofstickiness/tackiness. This, in turn, may result in the emulsion stick totires and may possible peel off the pavement. The present inventiveconcepts overcome these drawbacks in a number of ways. The describedasphalt-emulsion can be thicker, can adhere to the pavement better, canretain friction fine-aggregate better, and is more durable over time.The fine aggregate material can be applied to the emulsion on thepavement at increased rates. For instance, the fine aggregate materialcan be applied at least 1.0 lbs. per square yard, or higher.

On the pavement, the residue remaining from the broken and curedemulsion has a few special characteristics due to the gilsonite. Thepenetration into and softening of the aged oxidized underlying surfaceAC is enhanced by the gilsonite. Also, the gilsonite allows the additionof softer AC to the blend, which synergistically provides forrestoration of the underlying aged pavement's AC while simultaneouslynot being overly soft on the surface so as to be impractical as asealer. The gilsonite also is a natural antioxidant and is resistant toUV degradation.

The coating system yields a “typical” cure (e.g. 8-12 hours or more)with “decent” short-term friction results and excellent long-termfriction results. In particular, the emulsion cures in a matter of 8-12hours, or longer, depending on weather conditions, but the emulsionsystem appears to retain a high percentage of the frictionfine-aggregate. The friction numbers for the emulsion system tend tocontinue to steadily increase over time, eventually achieving or evenexceeding the pre-treatment friction numbers.

The inventive coating system delivers also all the benefits of fog sealbut with an increase concomitant with the increase in applied residue onthe pavement, e.g. from light up to medium application rates. Thecoating system is a long-term solution, believed to last 5 or moreyears. Furthermore, the coating system improves pavement condition bypenetrating and fusing with the pavement. The coating system does thiswhile also maintaining a relatively high amount of friction viahigh-performance CMFE test methods, not just initially but alsolong-term.

The coating system may be applied via in a convenient single-vehiclesystem. This limits contractor investment and labor costs and results ina system that can be applied more efficiently. Furthermore, the coatingsystem is suitable for use on high-speed runways and all other airfieldpavements (no limitations), or roadways.

Furthermore, the coating systems described herein are stable andbalanced enough to be applied at substantially higher amounts and stillprovide for the airfield pavement safety characteristics as well as alonger improvement in condition. However, unlike other treatments, thecoating system as described herein does not require an excessive blanketof aggregate spread over the binder. This removes the needed additionalsweeping operations to remove loose aggregate and generally being asafety issue for airfields.

The coating system does not require a liquid mixture of binder andaggregate and other fillers, which will eventually crack, delaminate anddeteriorate, creating safety issues. The described coating system can beapplied in a suitably thick layer such that it provides a more durableyet still safe surface coating with excellent friction characteristicsthroughout the extended life of the coating system.

The inventive coating system, and the emulsion in particular, can beeasily stored, shipped, and applied to the desired surface. Likewise,the inventive aggregate composition includes a fine, dense, angularhigh-friction aggregate material that is suitable for co-applicationwith the emulsion via a convenient vehicle-mounted spreader unit.Together these components are surprisingly effective for maintaining, oreven increasing the surface micro-texture and macro-texture roughness ofthe coating components while also providing increased durability.

It will be appreciated by those skilled in the art that variousmodifications and alterations of the present disclosure can be madewithout departing from the broad scope of the appended claims. Some ofthese have been discussed above and others will be apparent to thoseskilled in the art. The scope of the present disclosure is limited onlyby the claims.

The invention claimed is:
 1. A coating system for an airfield surface ora roadway, comprising: a stable cationic emulsion for application to theairfield surface or the roadway, the stable cationic emulsion having: a)an asphalt blend comprising gilsonite, wherein the gilsonite is modifiedto possess a positive charge; b) one or more polymers, and c) one ormore surfactants not including a cationic surfactant; and a fineaggregate material for application to the stable cationic emulsionapplied to the airfield surface or the roadway.
 2. The coating system ofclaim 1, wherein the asphalt blend comprises between about 50.0% toabout 70.0% by weight of the emulsion.
 3. The coating system of claim 1,wherein the gilsonite is present at level of at least about 20% byweight of the asphalt blend.
 4. The coating system of claim 1, whereinthe gilsonite is present at level of at least about 10% by weight of theemulsion.
 5. The coating system of claim 1, wherein the one or morepolymers is an acrylic, a styrene-butadiene rubber, or a combinationthereof.
 6. The coating system of claim 1, wherein the one or morepolymers comprises between about 1.0% to about 5.0% by weight of theemulsion.
 7. The coating system of claim 1, wherein the one or moresurfactants comprise between about 0.25% to about 4.0% by weight of theemulsion.
 8. The coating system of claim 1, wherein the one or moresurfactants is at least one of a non-ionic surfactant and an amphotericsurfactant.
 9. The coating system of claim 1, wherein the emulsion has amodifier present at level between 0.25% to 3.0% by weight of theemulsion.
 10. The coating system of claim 1, wherein the emulsion has apH less than 6.5.
 11. The coating system of claim 1, wherein the fineaggregate has a particle size distribution whereby substantially all ofthe particles pass through a No. 14 sieve.
 12. A coating system for anairfield surface or a roadway, comprising: a stable cationic emulsionfor application to the airfield surface or the roadway, the stablecationic emulsion having: a) an asphalt blend comprising gilsonite,wherein the gilsonite is modified to possess a positive charge; b) oneor more polymers, and c) one or more surfactants not including acationic surfactant; and a fine aggregate material for application tothe stable cationic emulsion applied to the airfield surface or theroadway; wherein the fine aggregate has: a particle size distributionwhereby substantially all of the particles pass through a No. 14 sieve;a fine aggregate angularity of at least 45% measured according to ASTMC1252 Test Method A; a bulk dry specific gravity of 2.6-3.0 measuredaccording to ASTM C128; and a Mohs hardness of at least 7.0 measuredaccording to ASTM MNL46.
 13. The coating system of claim 1, wherein saidfine aggregate material includes at least one of chert, quartzite, andcarbonate.
 14. The coating system of claim 1, wherein the asphalt blendcomprises between about 50.0% to about 70.0% by weight of the emulsion,and the gilsonite is present at level of at least about 10% by weight ofthe emulsion, wherein the one or more polymers comprises between about1.0% to about 5.0% by weight of the emulsion, and wherein the one ormore surfactants comprise between about 0.25% to about 4.0% by weight ofthe emulsion.